In recent years, there have been further developments in ubiquitous network environments that are accessible whenever and wherever. Specifically, getting popular are broadband networks including optical fibers and wireless networks including ad-hoc networks. Information appliances and other network-connectable devices are also getting popular.
Under these circumstances, there have been suggested the following three techniques as important techniques for ubiquitous networks. Namely, the three techniques are Network Seamless (also called Terminal Mobility), Device Seamless (also called Session Mobility), and Content Seamless (also called Media Adaptive).
Network Seamless is a technique for seamlessly switching a network to be accessed when a terminal moves between different networks. Device Seamless is a technique for seamlessly switching services and sessions between different terminals. Content Seamless is a technique for seamlessly switching to different media (including different formats and different media parameters).
Conventional techniques related to Session Mobility and Content Seamless will be described with reference to drawings.
Described first will be a technique related to Session Mobility accompanied by Content Seamless (for example, see IETF Internet-Draft “Session Initiation Protocol (SIP) Session Mobility” draft-shacham-sipping-session-mobility-01.txt, which is hereinafter referred to as the “IETF Internet-Draft”).
FIG. 1 illustrates conventional Session Mobility accompanied by Content Seamless. In FIG. 1, a switching source terminal 500 is receiving data related to an image delivery service from a media server 502. Then, using a SIP (Session Initiation Protocol) REFER 505 for example, the switching source terminal 500 instructs a switching destination terminal 501 to switch.
Upon receiving the switching instruction from the switching source terminal 500, the switching destination terminal 501 establishes a session with the media server 502 using, for example, a SIP INVITE 504. Specified in the Body of the SIP INVITE 504 is image resolution that can be handled by the switching destination terminal 501.
Upon receiving the SIP INVITE 504 from the switching destination terminal 501, the media server 502 establishes a session with the switching destination terminal 501. The session established here is a session in which the resolution specified in the Body of the SIP INVITE 504 is set.
The media server 502 transmits data related to the image delivery service, the data having the resolution specified in the Body of the SIP INVITE 504, to the switching destination terminal 501. The media server 502 then disconnects the session with the switching source terminal 500 using, for example, a SIP BYE 503. In this way, changing image resolution of image data in accordance with the capacity of the switching destination terminal 501, the media server 502 switches the session from the switching source terminal 500 to the switching destination terminal 501.
Described next will be a technique related to Session Mobility using a relay server, with a media relay method described in Japanese Patent Laid-Open Application No. 2004-248165 as an example.
FIG. 2 illustrates conventional Session Mobility using a relay server. The system shown in FIG. 2 has a communication terminal 600, a switching source terminal 601, a switching destination terminal 602, and a relay device 603. The relay device (relay server) 603 switches the connection from the connection between the communications terminal 600 and the switching source terminal 601 to the connection between the communications terminal 600 and the switching destination terminal 602. The relay device 603 then transfers media data (e.g. image data) delivered from the communication terminal 600 to the switching destination terminal 602. This procedure is shown in FIG. 3.
As shown in FIG. 3, the relay device 603 receives media data from the communication terminal 600 (S600), and transfers the media data to the switching source terminal 601 (S601).
The switching source terminal 601 then instructs the relay device 603 to perform session switching that switches a session of a currently used service (S602). Information on a session identifier and on an identifier of the switching destination terminal 602, for example, is notified as the session switching instruction.
The relay device 603 then transmits the media data received from the communication terminal 600 to the switching destination terminal 602 that is indicated by the session switching instruction as a switching destination terminal (S603).